1. Field of the Invention
The present invention relates generally to a wireless power receiver, and more particularly, to a wireless power receiver for increased charging efficiency.
2. Description of the Related Art
Mobile terminals such as mobile phones and Personal Digital Assistants (PDAs) are powered by rechargeable batteries that are charged with electrical energy by a separate charging device. Typically, a separate contact terminal is formed at the outer side of each of the charging device and the battery, which are electrically connected to each other through a contact between the two separate contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly and become easily contaminated by foreign substances and moisture, causing incorrect battery charging.
In order to solve the above-mentioned problems, a wireless non-contact charging technology has recently been developed and used in many electronic devices.
Such a wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged when placed on a charging pad without connecting the mobile phone to a separate charging connector. The use of the wireless charging technology is well known in a wireless electric toothbrush or a wireless electric shaver. The wireless charging technology improves a waterproof function since it wirelessly charges the electronic devices, and improves the portability of the electronic devices because it does not require a wired charger. It is expected that the development of technologies related to the wireless charging technology will be significantly furthered in the coming age of electric cars.
The wireless charging technologies are generally classified into an electromagnetic induction scheme using a coil, a resonance scheme using resonance, and a Radio Frequency (RF)/microwave radiation scheme for converting electrical energy into a microwave and transmitting the microwave.
Until now, the wireless charging technology using the electromagnetic induction scheme has been the mainstream. However, recent experiments in which power is wirelessly transmitted over a distance of several tens of meters by using microwaves have been successful at home and abroad. Accordingly, it is expected that an environment in which all electronic devices can be wirelessly charged anywhere and anytime will be realized in the near future.
A power transmission method using electromagnetic induction corresponds to a scheme for transmitting power between a primary coil and a secondary coil. When a magnet approaches the coil, an induced current is generated. A transmission side generates a magnetic field by using the induction current, and a reception side generates electrical energy by inducing a current according to a change in the magnetic field. This phenomenon is known as a magnetic induction phenomenon, and the power transmission method using this phenomenon has excellent energy transmission efficiency.
With respect to the resonance scheme, in 2005, a system was developed in which electricity is wirelessly transferred from a charging device to a device to be charged by using a power transmission principle of the resonance scheme known as a coupled mode theory even when the device to be charged is several meters away from the charging device. This wireless charging system employs the physics concept of resonance, by which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork will oscillate at the same frequency. An electromagnetic wave containing electrical energy was caused to resonate instead of causing sound to resonate. It is known that the resonant electrical energy does not affect surrounding machines and human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device having a resonance frequency, and its unused part is reabsorbed into an electromagnetic field instead of spreading in the atmosphere.
A wireless power receiver according to the related art includes a Direct Current (DC)/DC converter for DC/DC converting charging power which has been received and rectified, and a charger for delivering the DC/DC converted charging power to a charging unit. Specifically, the wireless power receiver according to the related art independently includes the charger and the DC/DC converter, and thus has a problem of an increase in mounting area.
Moreover, the wireless power receiver according to the related art has a problem in that the two independent units may reduce overall charging efficiency. Specifically, the charging efficiency of the wireless power receiver according to the related art is determined by the efficiency of the DC/DC converter multiplied by that of the charger. Accordingly, the overall charging efficiency is reduced. Therefore, it is required to develop a wireless power receiver which enables a reduction in the mounting area together with an increase in the overall charging efficiency.
In this regard, a need exists for a wireless power receiver including a power processing Integrated Chip (IC) that serves as a charger simultaneously with performing DC/DC conversion, and a control method thereof.